The construction of orifice plates is a critical aspect of ink jet printers, and various materials and fabrication techniques have been utilized toward attaining desired dimensional preciseness and physical durability (e.g. against chemical attack or abrasion) for those critical elements. One highly useful approach described in U.S. Pat. No. 4,184,925 is to electroplate a metal, e.g. nickel, over a photoresist peg pattern on a mandrel for a period of time such that the openings over the photoresist pegs have been closed by the nickel to the exact diameter desired for the orifices. The orifice plate is subsequently thickened by forming another photoresist peg over the newly defined orifice (on the opposite side from the first peg) and electroplating with nickel to a final overall thickness of about 7.5 mils. Orifice plates fabricated according to the '925 patent teaching have been used in both continuous and drop-on-demand ink jet printing with good results.
In continuous ink jet printers the orifice plates receive acoustic stimulation to regulate drop break-up of continuous ink streams issuing from the orifices. This stimulation can be of the traveling wave or plane wave kinds (see, for example, U S. Pat. Nos. 3,822,508 and 4,646,104). The plane wave stimulation offers the advantage of more synchronous break-up of the jets of a linear array because the orifice plate is vibrated in a nominally planar state, e.g. in the directions of the jet streams. This reduces the necessary drop charging window in comparison to what is needed for the non synchronous drop break-up that is characteristic of traveling wave stimulation.
However, I have found that problems can occur when orifice plates, such as described in the '925 patent, are used in long array (e.g. about 4 inch) orifice plates stimulated via the planar wave approach. Specifically, for good acoustic transmission, orifice plates that are thicker and acoustically stiffer than those of the '925 patent are needed. The problem is compounded because the longer arrays must continue to be highly flat, and increasing the thickness of electroforms, such as in the '925 patent, tends to produce bowing because of incorporated tensile stresses.